The genetic hypothesis of susceptibility to the systemic from of leprosy assumes an inborn defect in mesenchymal cells. So far there exists no valid animal model for the study of leprosy as occurs in man. Nine-banded armadillos have propitious characteristics for establishing such a model, particularly because of their longevity and monocygous quadruplet litters. Our previous experiments have shown that leprosy-susceptible armadillos occur. If successful breeding in captivity could be accomplished, with known non-leprous susceptible and resistant armadillos, animal models could be established for a broad study of fundamental and applied aspects of leprosy in man. The objectives of this study are to attempt breeding based on better knowledge of anatomy of reproductive organs, reproductive physiology of male and female armadillos and to devise a quick and reliable test for susceptibility. The latter will be based on viability of leprosy bacilli in the tissues of armadillos, the nature of their cell response to their presence and to other substances, as well as on their capability to develop delayed type hypersensitivity to M. leprae and simple chemical compounds.